The IALA A Buoyage System Mnemonics
The red and green marks correspond to the red and green steaming lights (of your own vessel) when entering a channel.
Preferred Channel Marks
The preferred channel marks mostly correspond to the appropriate marks on the side of the preferred channel.
The "preferred channel to starboard" buoy (left) has the same shape, topmark and almost all of the colour of a port-hand buoy which means it is primarily left to port (pass it to starboard). The green band indicates that it could also be viewed as a starboard buoy.
The system for cardinal marks has several mnemonics associated with it.
The north and south top marks point to the top (north) and bottom (south) of a chart. The west and east marks can be seen to contain a W and E shape (see right).
Alternate mnemonics are:
West = Wasp-Waisted Woman or Wineglass shape
East = Easter Egg-shaped
Cardinal marks are warning marks and the black and yellow colours are like the warning bands of a wasp.
The top marks point to the black stripe/s of the buoy.
Lights are based approximately on a clockface.
North: quick flashing or very quick flashing
East: three o'clock = group flashing three
South: six o'clock = group flashing six plus one long flash
West: nine o'clock = group flashing nine
Isolated Danger Mark
Isolated danger marks are coloured in black and red stripes, red and black often indicating danger (think of Dennis the Menace). As for the top marks, just think of "balls-up" which is what will happen if you come too close to one.
The light is always "group flashing 2", two for the two balls.
Safe Water Mark
Until the emergency wreck buoy came along (see below), there was an unofficial rule that vertical stripes meant danger and horizontal stripes meant safety. This no longer applies. Also, a ball marks danger in both the isolated danger buoy and on ships' day marks. So the safe water buoy is not immediately obvious as a "safe" mark.
New Wreck Mark
The "new wreck" mark does not fit neatly with the existing buoyage system. Blue-and-yellow is not a sign of danger in normal circumstances; the vertical stripes diverge from the horizontal danger stripes of other buoys, and a cross top mark is not clearly a danger signal (an angled cross, like an X, would be more obvious).
However, this unusual combination does have the advantage of making the buoy distinctive. And, since by definition, they do not appear on older charts (being a new wreck), this distinction makes them stand out from the crowd. You could think of the cross as marking a grave (of a ship).
The special mark is unlike all the others, having a yellow colour and yellow light, so is immediately obvious.